Defrosting and frost prevention



' Miami 7, 1944.

M. S. SCHECHTER ET AL DEFROSTING AND FROST PREVENTION Filed Aug. 51, 1940 &

ZSnventors MS. SCHEC-HTER H. L. \J. HALLER (Ittorneg without the payment to 'densed from the air for such a length of time Patented Mar. 7, 1944 2,343.246 DEFROSTING AND FROST PREVENTION Milton S, Schechtcr and Herbert L. 3. Keller, Washington, D. C.

Application August 31, 1940, Serial No. 354,949

(ill. 62-403) Claims.

(Granted under the act of March 3, amended April 30, 1928; 370 0.

This application is made under the act of March 3, i883, as amended by the act of April 30, 1928, and the invention herein described and claimed, if patented, may be States of America for governmental purposes us of any royalty thereon.

This invention has for its chief object the provision of a method for eliminating frost and ice formations on the cooling or heat exchange units of refrigerating systems. Another object of this invention is the provision of a method for defrosting the cooling units of refrigerating systerns and for maintaining them free of frost and ice during the operation of the refrigerator without shutting off the refrigerating machinery. Other objects will beapparent from the description hereafter given.

.Frost as used in this description includes Ice.

The deposition of frost on cooling or heat exchange units, such as refrigerant coils, pipes, and other heat exchange elements, is a well-known phenomenon. It is caused by the distillation of water from the-materials undergoing refrigeration to the heat exchange unit, and moisture conbelow the dew point of the ambient air. Frost being a relatively transfer of heat between the surrounding atmosphere and the heat exchange unit is greatly hindered by the frost and consequently the efflciency of refrigeration is significantly lowered. In order to compensate for a poor transfer of heat through the frost, the heat exchange unit must be kept at a temperature lower than what would otherwise present, thus putting a heavier load on the refrigerating machinery. ing up of layers of frost on heat exchange units necessitates some method of defrosting the units from time to time, which is both expensive and time-consuming. Some of the common methods of defrosting now in use are:

1. Shutting down the frlgerating machinery t the heat exchange in the refrigeration compartment when the temperature of the evaporator is poor conductor of heat, the

Furthermore, the buildmanufactured and used by; or for the Government of the United be necessary if such frost were not i unit can warm up sufllclently to permit the frost to melt. v

2. Removing the frost from the cooling unit by mechanical means, such; as c opplng, scraping. and so forth.

3.- .Attempting to preventfrost formation on the cooling unit by the use of special paints.

Besides being both time-consuming and ea- 1883, as G. 757) pensive, none of these methods has been found to be wholly satisfactory.

We have discovered that frost on a heat exchange unit can easilybe removed and its formation on the unit easily prevented by a simple and inexpensive process which comprises, generally, the placing of a suitable vessel containing a volatile liquid miscible with water in whole or in part in proximity to the cooling or heat exchange unit The liquid should be volatile enough to distill from the container to the cooling unit under the small temperature differential prevailing between the unit and the surrounding air. Some of the liquids which have been found to work well in the process are methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, and diethyl ketone. Mixtures of liquids can also be used. The foregoing examples are merely illustrative of the liquids which may be used in the process, and this invention is not to be considered limited thereby. Also, this invention is not limited to the use of alcohols or ketones or mixtures thereof, for although these types of compounds have been found to work most satisfactorily, other classes of compounds may also be used.

Our novel process depends for its succem on the fact that a compound will distill from a warmer region to a cooler region. It also depends on the fact that, in general, a relatively small amount of a compound will lower the freezing point of a liquid when dissolved in it. Thus, in the defrosting process, the volatile liquid distills from the container to the cooling unit because of the difference in temperature between the two, even though the difference is slight. Upon coming into contact with the frost on the cooling unit, the condensed liquid causes the frost to melt. due to the lowering of the melting point of the frost by the presence of the liquid which has distilled. The condensed liquid, together with the melted frost, then falls off the cooling unit. (The process of defrosting is believedto take place as outlined above. However, this invention is not any manner by the so as to receive from it the melted frost plus con...

densed volatile liquid from the cooling unit, the volatile liquid in the container will progressively become more and more dilute until it finally loses its full effectiveness. We have innovated modilications of our process which greatly minimize this dilution effect.

One" modification of our process. comprises placing in the vessel, in addition to the volatile I liquid, a water-soluble compound or material tainer may be returned to the second vessel,

thereby making the system regenerative with respect to the volatile liquid.

capable of salting out the volatile liquid from an aqueous solution thereof. Water-soluble compounds suitable for use in this modification of the process are sodium chloride, sodium carbonate, sodium sulfate, sodium dihydrogen phosphate, disodium phosphate, potassium chloride, potassium carbonate, potassium sulfate, potassium dihydrogen phosphate and dipotassium phosphate. 1 These compounds are cited merely by way of illustration and not by way of limitation, since any water-soluble compound capable of establishing a salting out effect on the liquid used in the process may be employed. The function of the compound so ,used is to cause a separation of the mixture inv the container into two phases, namely, a lower phase consisting essentially of an aqueous solution of the compound and an upper-phase consisting essentially of the volatile liquid. The volatile liquid is thus kept floating as the upper phase and is maintained practically undiluted by the melted frost from the cooling unit. for continued use in the process. The lower phase can be drawn off whenever necessary and discarded or, if desired, the compound dissolved therein, may be recovered and returned to the system by evaporating the water.

Another modification of our process comprises placing in the vessel, in addition to the volatile liquid, 2. compound or material which will dehydrate, in whole or in part, the liquid used in the process. Compounds or materials suitable for use in this modification are anhydrous sodium carbonate, anhydrous sodium sulfate, anhydrous potassium carbonate, anhydrous magnesium sulfate, anhydrous calcium sulfate, calcium chloride, calcium oxide, barium oxide, anhydrous copper sulfate, and activated aluminum oxide. These compounds are citedv merely by way of illustration and not by limitation and it is to be understood that this invention is not limited thereby. Any drying agent capable of This invention can be varied in many ways.

For example, two vessels may be used instead of one. One vessel may be used to catch the drippings, while the other vessel with the volatile liquid, is placed at some other point in the refrigerator. The first vessel, if desired, may contain a compound capable of efiecting a salting out reaction or it may contain a compound or material having dehydrating or drying properties in order to remove water from the drippings, but the useof such compounds isfnot indispensable, since the full strength of the volatile liquid will be retained in the second vessel.

Where such modifications are employed, a drain.

pipe from the lower phase in the first vessel to the exterior of the refrigerator housing may be employed, so that this phase may be drawn off from time to time. Also, a pipe connection may be used between the upper phase of the first vessel and the second vessel, so that salted out or dehydratedvolatile liquid in the first con- Consequently, it is available In the accompanying drawing there is illustrated the modification of our invention in which two vessels are employed. The drawing is a vertical section of a refrigerator box I containing the usual cooling coils or heat exchange unit 2. Below the unit 2 there. is disposed a vessel 3 for catching the drippings from the unit 2. At another point in the box there is disposed another vessel 4 containing the'volatile liquid. In the drawing, this vessel 4 is placed directly beneath the vessel 3. However, any point in the refrigerator is suitable so long as the vessel 4 is kept free from dilution. The vessel 3 is provided with either a salting out or a dehydrating compound for the purposes mentioned above, and an overflow 5 from'the vessel 3 to the vessel 4 is provided. Also, a drain pipe Shaving a valve I is connected to the vessel 3 to draw oil, occasionally, excess quantities of the lower phase.

Having thus described our invention, we claim:

1. In combination with a refrigeration system having an evaporator unit, said evaporator being disposed in a compartment, a vessel beneath said unit to catch drippingsv therefrom, another vessel in the compartment at a region normally warmer than the evaporator containing a volatilawatermiscible liquid.

2. In combination with a refrigeration system having an evaporator unit, a vessel beneath said unit to catch drippings therefrom, said vessel having an overflow at the top and a drain pipe at the bottom, a second vessel beneath said firstmentioned vessel in a region normally warmer than the evaporator, whereby when a volatile water-miscible liquid is placed in said second vessel it will evaporate and condense on the evaporator, and whereby said first-mentioned vessel will catch drippings from said evaporator.

3. The method of defrosting and of preventing the formation of' frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the yapor of a. water-miscible liquid.

4. The method of defrosting and of preventing the formation of frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of a volatile liquid chosen from the group consisting of water-miscible alcohols and water-miscible ketones.

5. The method of defrosting and of preventingthe formation of frost on the evaporator of a the formation of frost on the evaporator of a I refrigeration system surrounded by humid air, comprising mixing the air with the vapor of a. ketone chosen. from the group consisting of acetone, methyl ethyl ketone, anddiethyl ketone. 7. The method'of defrosting and of preventing the formation of frost on the evaporator .of a

refrigeration systemsu'rrounded by humid air,

- comprising mixing the air with the vapor of vapor of a refrigeration system surrounded by humid air,

with the vapor of comprising mixing the air n-propyl alcohol.

10. The method of defrosting and of preventing the formation of frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of isopropyl alcohol.

11. The method of defrosting and of preventing the formation of frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of acetone.

12. The method of defrosting and of preventing the formation of frost on the evaporator of aaoaaoo a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of 'methyl ethyl ketone.

13. The method of defrosting and of preventing the formation of frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of diethyl ketone.

14. The method of defrosting and of preventing the further formation of frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of a water-miscible liquid.

15. The method of preventing the formation .of frost on the evaporator of a refrigeration system surrounded by humid air, comprising mixing the air with the vapor of a water-miscible liquid.

MILTON S. SCHECHTER. HmBERT L. J. HALLER. 

